Conventionally, a refrigerating cycle apparatus which is applicable to an air-conditioner is developed, and an outdoor heat exchanger of the refrigerating cycle apparatus may be operated as an evaporator. In such a case, when a refrigerant evaporation temperature in the outdoor heat exchanger becomes lower than or equal to the freezing point (0° C.), frost may arise in the outdoor heat exchanger.
If the frost closes a passage of outside air in the outdoor heat exchanger, the heat exchange performance of the outdoor heat exchanger will decrease. That is, the amount of heat absorbed by refrigerant from the outside air in the outdoor heat exchanger will decrease, and air to be sent cannot fully be heated, as a refrigerating cycle.
JP 2015-33953 A describes a refrigerating cycle apparatus in which a defrosting operation is performed for removing frost generated in an outdoor heat exchanger. When the defrosting operation is conducted for the outdoor heat exchanger (evaporator), an opening degree of the expansion valve as a pressure reducing device is increased to a middle position which is set experimentally in advance. Thereby, frost of the outdoor heat exchanger can be melted by hot gas which is refrigerant discharged from the compressor.